Coolant question

[Christien]

Technical, but non Porsche-related. Last night I noticed the temperature gauge in our 2005 Honda Odyssey was at full, after about 15 minutes of highway driving. I immediately pulled over and stopped and let the engine cool down. I didn't notice any signs of a leak, and I put 2 L of tap water in there. I continued driving for another 2 hours at highway speeds, and the temperature gauge read normal the entire way, even with the a/c on.

Not knowing anything about coolant (I've only done serious wrenching on 911s), how urgent is it that I flush the water and replace with proper coolant? Doing some Google research while waiting for the engine to cool down, I learned that it's not uncommon for cars to have a slow leak of coolant over time that doesn't really need to be repaired, just topped up. The van has 177k km, and judging by other maintenance items I found (or lack thereof) when we bought it at 125k, it wouldn't surprise me if the coolant system had never been addressed. So I don't think we have any imminent failure of either hoses or the water pump. But from what I understand, I can't just leave the water in there permanently.

[sammyg2]

Ordinarily i would say don't sweat it that much unless it's winter-time, but Hondas are really funny when it comes to liquids.
that's partly why I'll never own another honda.

[1990C4S]

Do it before December.

Use the Honda coolant, and don't use tap water.

[Noah930]

I have also always been advised to use Honda cooolant. If you have to top off with water, try to use distilled, instead of tap water (mineral content). Inhaven't done it on our Odyssey, but it was a pretty simple process in our Civic to drain and fill 3 or 4 times for a coolant flush. I did the initial flushes with distilled water, and just used a gallon of Honda coolant for the final fill. I think Honda calls for 100k miles (and each 50k miles thereafter) for coolant changes. You probably don't have to do it immediately, but I'd do it at some point in the near future.

[manbridge 74]

Last gallon of Honda coolant I saw said it 50/50 coolant and demineralized water. Guess they one upped the distilled water used by others.

We used to use demineralized water to store our probes in when I was involved in various water treatment duties. Left no deposits.

I'd just change it all out if you want to keep the van. Not a whole lot of money.

[RANDY P]

I wouldn't sweat it, especially if you can drink the tap water. But do check the water levels again, it will self-bleed and likely go low. Get the engine hot, fill the reservoir (not the radiator, the reservoir) to Full Hot- if there is such a thing, with the heater on full blast.

it'll be OK.

rjp

[Neilk]

Originally Posted by 1990C4S

Do it before December.

Use the Honda coolant, and don't use tap water.

Did you see where he lives? I would say do it before October!

[1990C4S]

He lives pretty close to where I used to live. He's in a better part of town, but no warmer.

[Christien]

Thanks guys. The issue is having it freeze overnight, right? Not really any chance of that until December at the earliest, and even then, that's pretty rare. We've had green Christmases for years now, except this year where we had a crazy cold December followed by the mildest winter I can remember.

I'll get it changed out in the next couple weeks. My question was more of urgency based on convenience and when I've got some time off to do some work on cars. If it was really urgent, like day to day, I'd find time to do it tomorrow, but if it can wait, I'll do it when I'm off later this month.

Thanks!

[Christien]

Oh, and to add to the peculiarities of Honda fluids, I was advised by many people that Honda ATF is specific, and to use it, and only it. It's a bit more expensive than regular, but not crazy, but apparently to use generic stuff can really cause problems with the tranny. So to hear that I should use only Honda coolant doesn't surprise me.

[Sooner or later]

How did it lose two liters of water?

[Christien]

Good question. There were no signs of a leak - no steam, no noise, no smell, just a high temp gauge. I've read that it can be a slow leak over time. Maybe there was enough in it to keep it cool until just a few days ago. It hasn't been a hot summer, so it's been getting cool air and little a/c use.

[Evans, Marv]

I've always understood part of the importance of using a coolant mixture was for its lubricating properties (water pump for one thing) and the fact it can hold more heat in terms of calories than water by itself (don't know the validity of that though). I can't actually understand why you would be using water only. An off the wall thing that sort of matches the symptom your car had was something a friend of mine had. The car would apparently over heat occasionally. If she stopped and shut it off for awhile, it would be OK. Turns out she had the coolant changed and the change left an air bubble in the area of the heat sensor that would seem to be circulated around and occasionally settle on the sensor and register an overheating situation. She had the coolant changed again & the problem went away. I had a hard time believing it, but couldn't deny the problem disappeared after the coolant change.

[Noah930]

It can wait.

Honda coolant is about the same cost as the rest of the stuff at your FLAPS. And you only need a gallon of it (or at least that's all that fit into my Civic). It comes pre-mixed. Honda no longer makes/sells the concentrated stuff.

[ckelly78z]

You need to figure out where the coolant leaked out, and fix that first. Leaving plain water in a cooling system will pre-maturely rust thje radiator, and any steel coolant passages if left in there without the proper mixture of coolant. There is the added benefit of the lubrication properties of the coolant over regular water, but the rust issue will soon become a problem.

[javadog]

I will add to the comments above and if you have a leak, and you do, you can also reduce the effectiveness of the cooling system because it may not pressurize properly. Apart from finding the leak, I would also pressure test the cap.

Contrary to what was posted above, pure water does a better job of rejecting heat versus coolant. You do need the coolant though, because of the higher freezing point of water, and anti-corrosion and lubricating properties of some of the additives in the coolant.

[Christien]

It overheated again today, so there's definitely a leak. Great.

[flipper35]

Heater cores can be a painful source of the coolant leak.

Yes, water alone is far better at transferring the heat from the engine, through the radiator to the air. When i lived in the desert I used water and water wetter additive because the water wetter added the lubrication and anti-corrosion necessary. Most of the circle trackers here use just water since they flush it often. Never understood that.

[VincentVega]

I had a honda van with a cracked reservoir recently, small crack but it leaked. Fill it up and pressurize, you'll see where its leaking if its external.

good luck

[1990C4S]

Get a pressure test.

Does your oil look okay?

I would be worried about the head gasket if there are never any drips.